Paying for It
I have been taking Yuval Noah Harari's Coursera course A Brief History of Humankind, which takes a long term view of the human story. Prof Harari is very much of the evolutionary point of view, and he frequently emphasizes that some of the deepest puzzles of human history are posed by those evolutionary questions.
What, for example, is the point of a big brain if you have only the most primitive tools and weapons, and are stuck down somewhere in the middle of the food chain. It's three per cent or so of our body weight costs us 25% of our energy usage, for example, and it is burdensome to carry around with all their accompanying packaging. Everything in evolution, he likes to say, has a cost. We pay for the big brain by needing to eat more and by sacrificing much of our muscles. We are incredibly puny, for example, compared to a chimpanzee of the same weight.
One argument he makes that I find less persuasive - so far, anyway - is that because humans have been top predators for only a short time, about 100,000 years, we haven't yet learned, or rather evolved, how to manage that position.